Update mime-types dependency

maid.gemspec

@@ -22,7 +22,7 @@ Gem::Specification.new do |s|
  s.add_dependency('thor', '>= 0.14.0', '< 1.0.0')
  s.add_dependency('deprecated', '~> 3.0.0')
  s.add_dependency('dimensions', '>= 1.0.0', '< 2.0')
- s.add_dependency('mime-types', '~> 2.0')
+ s.add_dependency('mime-types', '~> 2.0', '< 3.0') # 3.0 drops Ruby 1.9.3 compatibility (which should be kept for Ubuntu, at least until we document use of Maid on 2.0+ for Ubuntu). mime-types 2.99 is supported until 2017-11-21. https://github.com/mime-types/ruby-mime-types/#mime-types-2x-end-of-life
  s.add_dependency('rubyzip', '~> 1.1.0')
  s.add_dependency('xdg', '~> 2.2.3') # previous versions had bugs
  s.add_dependency('listen', '>= 2.8.0', '< 3.1.0')